What are the two main energy sources that drive the Earth’s processes?

Solar radiation from the Sun, which powers surface processes such as photosynthesis, the water cycle, winds and weather; and the Earth’s internal heat working with gravity, which powers the interior and drives plate tectonics. Sunlight dominates the surface while internal heat drives the deep Earth.

Where does the Earth’s internal heat come from?

From two sources: primordial heat left over from the planet’s formation (collisions during accretion and the sinking of the iron core) and radiogenic heat produced continuously by the decay of radioactive isotopes such as uranium, thorium and potassium. Current estimates put the two in broadly comparable shares, though the exact split is uncertain.

What drives the movement of tectonic plates?

Internal heat and gravity together. Heat drives slow convection in the solid mantle, but the strongest force is generally thought to be slab pull — gravity dragging a cold, dense subducting plate downward, pulling the rest of the plate with it — helped by ridge push. Plates with long subducting edges move fastest, supporting slab pull as the leading driver.

Why does the Earth have plate tectonics when the Moon and Mars do not?

Earth is large enough to retain plenty of internal heat, contains enough radioactive elements to keep generating it, and has a lithosphere that breaks into mobile plates. Smaller bodies such as the Moon and Mars cooled relatively quickly and became single-plate worlds. On Mars, a stationary crust let one hotspot build Olympus Mons, the largest volcano in the solar system, whereas Earth’s moving plates spread eruptions into chains like Hawaii.

The engines driving the Earth

Every Earth process — a growing forest, a falling raindrop, a rising mountain — needs energy to drive it, and it comes from one of just two engines: the Sun overhead, or the Earth's own heat below. This powerbook sorts out which engine powers what, where the planet's inner heat comes from, and how heat and gravity turn into moving continents.

energy engines

sources of inner heat

short sections

The engines driving the EarthSection 1 of 5

0 of 5 locked in

This book has 5 short sections. Read each one, answer the check, then use Next to move on — the bar above tracks how far you've come.

The planet runs on two engines

Nothing on Earth happens for free. Rivers flow, plants grow, winds blow, mountains rise — every one of these is a process, and every process needs energy to drive it. The whole of this module is really one question: where does that energy come from? The answer is that the Earth runs on two quite different engines.

One is outside the planet: the Sun. Solar radiation pours onto the surface and powers almost everything that happens there — the warmth, the weather, the water cycle, and the green machinery of life. The other engine is inside the planet: the Earth’s own internal heat, left over from its birth and still being topped up, working together with gravity. This is the engine that stirs the deep interior and shoves the plates around.

Keep the two apart and the module clicks into place. Sunlight is the surface engine; internal heat is the interior engine. They barely overlap — plants do not care what the mantle is doing, and the plates do not run on sunlight. Almost every Earth process you can name is powered by one engine or the other, and the first job is simply to know which.

Two engines: sunlight drives the surface from outside; the Earth's own heat drives the interior from within.

New words

solar radiation

Energy from the Sun — the dominant engine of the Earth’s surface.

internal heat

Heat inside the Earth, working with gravity — the engine of the deep interior and the plates.

🔒 Lock it in

What is the cleanest way to organise the many processes happening on and in the Earth?

Answer the check to continue

Quick reference & sources

The interactive book above is the lesson. What follows is a plain recap you can revise from, plus the sources and how this maps to the syllabus.

Two engines, two domains

Solar radiation powers the surface — photosynthesis (the base of food chains), the water cycle, and the winds and currents that make weather and climate. It delivers thousands of times more energy to the surface than internal heat does. Internal heat plus gravity powers the interior — driving mantle convection and the movement of tectonic plates.

Where the internal heat comes from

Two sources. Primordial heat is left over from formation — accretion impacts and the sinking of the iron core. Radiogenic heat is made continuously by the decay of uranium, thorium and potassium. Current estimates put them in broadly comparable shares (the exact split is uncertain), and the ongoing radiogenic heat is why the Earth has not cooled to a dead lump. The mantle is hot solid rock that creeps slowly — not molten liquid.

Heat and gravity move the plates

Heat drives slow mantle convection, but the strongest driver is generally slab pull — gravity dragging a cold, dense subducting plate down and pulling the rest behind it — assisted by ridge push. Evidence: plates with long subducting edges (Pacific, Nazca) move fastest. Earth is the only solar-system body with modern plate tectonics; smaller, cooled bodies like the Moon and Mars are single-plate worlds (a still Martian crust built Olympus Mons; Earth's moving plate built the Hawaiian chain).

For HSC students

This powerbook covers the Role of Energy in the Earth’s Processes thread of Module 3 (Energy Transformations), framed by the inquiry question how does energy drive the Earth’s processes? Working through it, you should be able to:

analyse the role of solar radiation in driving surface processes such as photosynthesis and the water cycle;
identify the sources of the Earth’s internal heat (primordial and radiogenic);
investigate the role of gravity and heat in plate movement, and describe the contributions of convection and slab pull to plate speed;
compare the movement of the Earth’s plates with the surfaces of other solar-system bodies such as the Moon and Mars.

The practical for this topic is to demonstrate convection currents (for example, watching colour move through a heated liquid). The geological events these energies produce — earthquakes, volcanoes and mountain ranges — are the next chapter. Explanations here are original and are a study aid, not a copy of the syllabus.

Sources

US Geological Survey, This Dynamic Earth — internal heat, mantle convection and plate-driving forces.
NASA planetary science overviews — comparative tectonics and volcanism of the Moon, Mars (Olympus Mons) and Earth (Hawaiian hotspot chain).
Geoscience Australia and standard geophysics references — sources of the Earth’s internal heat (primordial and radiogenic) and the roles of convection, slab pull and ridge push.
NSW NESA Earth and Environmental Science Stage 6 Syllabus (2017) — used only to scope the Module 3 content; explanations above are original.

Keep going

One engine in the sky, one in the deep. Sunlight runs the living surface; leftover and home-made heat, with gravity, runs the restless interior — and almost everything the planet does is the work of one or the other.